1. Field of the Invention
The present invention generally relates to an electrostatic chuck for semiconductor wafers, and more particularly to an improved chuck that can operate over a broad range of temperatures and pressures.
2. Description of the Prior Art
Electrostatic chuck technology is vital to the future of semiconductor plasma processing. Such chucks eliminate the need for mechanical clamping devices for holding the semiconductor wafer; devices which are clumsy and can introduce contamination into the processing chambers.
There have been a number of prior art proposals for electrostatic chuck designs, including the following:
Japanese Patent No. 62-264638 to Toto Ltd., discloses a conductor layer and an insulating film made of ceramics capable of plastic deformation that are successively piled on a ceramics green sheet to form a piled material. Then, this piled material is fired to obtain an electrostatic chucking substrate.
U.S. Pat. No. 4,645,218 to Ooshio et al., discloses an electrostatic chuck with channels for passing a cooling medium through the body of the chuck.
U.S. Pat. No. 4,897,171 to Ohmi, discloses a wafer susceptor which has a first conductive electrode including a flat surface covered with a thin insulating film and a second conductive electrode which is electrically insulated from the first conductive electrode and is disposed so that a surface thereof is flush with the surface of the thin insulating film which covers the first conductive electrode
European Patent No. 0360529 to Toto Ltd., discloses an electrostatic chuck with at least two layers, each including an electrically insulating film and an electrode attached to a lower surface thereof and at least two layers being disposed as attractive layers on the base plate. A voltage applying assembly selectively applies a voltage to at least one of the electrodes to electrostatically attract the object to the insulating film of an uppermost one of the layers.
In general, prior art electrostatic chuck designs have not been altogether satisfactory in their operation, particularly when judged on their ability to operate over-broad temperature and pressure ranges extending down to cryogenic temperatures.